One of the most difficult endeavors in the laboratory environment, particularly involving pharmaceuticals, biology, chemistry or medicine, is the placement of minute volumes of liquid onto substrates for subsequent processing. Volumes of liquid in the order of 100 nanoliters or less have negligible weight, are susceptible to ambient fluidic currents, may have an ionic bias and may have surface tension which is large compared to its overall weight. The net effect is that it is extremely difficult to precisely deposit such small volumes on a test plate.
To further complicate the matter, in many laboratory environments, the placement of such small volumes must simultaneously occur a relatively large number of times. For example, multi-probe dispensing heads are known which can dispense simultaneously 48 aliquots, 96 aliquots or even greater numbers at a single instance.
Typically, these multi-probe heads are robotically manipulated and include a large number of needles oriented in an array for simultaneous movement from a loading site to a dispensing site and then to a washing site. Applicant has discovered that one of the factors leading to unreliable liquid transfer, particularly at ultra low volumes includes anomalies that exists with respect to the tips of the needles' location vis-à-vis the underlying surface that is to receive the ultra low volume of liquid. That is to say, when an array of 48, 96 or other number of probes are to contact and deliver an ultra low volume of liquid simultaneously, it is essential that the tips of all the syringe probes contact the receiving surface uniformly in order to assure optimal fluid transfer. If one or more of the needle tips of the probe assembly are not touching the receiving surface, the transfer of liquid can not be assured particularly as to the non-touching tip since the liquid will display an affinity to remain on the tip rather than transfer onto the underlying receiving surface.